Hydraulic dampers are used in many situations where it is desired to isolate sources of vibration or to protect sensitive equipment from shock and vibration. Examples include, but are not limited to, industrial equipment and machinery isolators; industrial robotics; building, bridge and ship isolators; military weapons systems; agricultural equipment; and construction equipment. Hydraulic dampers are also often used as mounts to control movement of vehicle powertrains in response to forces, such as reaction torque and vibration. The mounts also isolate engine vibration from the body of the vehicle.
A well-known type of hydraulic vibration damper is a magneto-rheological (“MR”) damper, which utilizes magneto-rheological (MR) fluids in conjunction with at least one magnetic field generating device. MR fluids typically comprise ferromagnetic micro-particles suspended in a low viscosity carrier fluid. When the MR fluid is exposed to a magnetic field, the micro-particles suspended in the carrier fluid align in a chain-like structure parallel to the applied magnetic field, resulting in an increase in the apparent viscosity of the fluid. The apparent viscosity of the MR fluid increases in proportion to the strength of the magnetic field. Thus, the damping effect of the shock absorber can be adjusted by varying the strength of the applied magnetic field.
Adjustable shock absorbers utilizing MR fluids and magnetic field generating devices used in motor vehicles are typically a single- or dual-cylinder design having a cylindrical housing, a piston slideably within the housing, a piston rod connected to the piston, a fluid reservoir located within the housing and containing MR fluid, a magnetic field generating device, a series of valves to control MR fluid flow within the housing, and at least one closing system. The closing system is located on at least one end of the damper housing. The functions of the closing system include, but are not limited to, providing a piston rod guide to support reciprocal motion of the piston rod, providing lubrication for the piston rod, retaining the MR fluid within the fluid reservoir, and preventing foreign contaminants from entering the damper.
Lubrication of the piston rod is desirable to facilitate smooth actuation of the piston assembly, reduce heat generation, reduce wear, and extend the life of the damper. Unfortunately, lubricating systems are cumbersome, adding to the cost of the damper. In addition, the constant motion of the piston rod when the damper is in service will eventually exhaust the lubricant due to limitations inherent in piston rod seals that permit small amounts of lubricant to escape around the piston rod seal. MR fluid may be used as a lubricant, as the carrier fluid portion of MR fluid is a suitable lubricant. However, the micro-particles in the MR fluid can have an abrasive effect on the piston rod and piston rod guide as the piston rod moves reciprocally in the piston rod guide. Accordingly, there is a need for a simple lubricating and sealing system for MR dampers that will provide long life, reduced wear, and adequate lubrication of the piston rod without the need to periodically replenish the lubricant.